The present invention relates to xcex1,xcex2,xcex2-trisubstituted hydroxylamines, referred to hereinbelow as alkoxyamines, obtained from xcex2-phosphorous nitroxides, which may be used in particular as free-radical polymerization initiators. The use of alkoxyamines such as those derived from 2,2,6,6-tetramethylpiperidyl N-oxide (TEMPO) in the preparation of macromolecules has given rise to many publications.
Thus, Hawker C. J. et al. (Macromolecules 1996, 29, pages 5245-5254) showed that the use of alkoxyamines derived from TEMPO such as (2xe2x80x2,2xe2x80x2,6xe2x80x2,6xe2x80x2-tetramethyl-1xe2x80x2-piperidyloxy)methylbenzene as free-radical polymerization initiators of styrene make it possible to control the polymerization and to gain access to well-defined polymers with low polydispersity indices, and they have found that the polymerization rates are substantially equivalent to the rates obtained when conventional initiators such as AIBN or benzoylperoxide are used in the presence of TEMPO.
It has now been found that the use of alkoxyamines derived from xcex2-phosphorous nitroxides as polymerization or copolymerization initiators for at least one monomer which may undergo a free-radical polymerization affords excellent control of the polydispersity while at the same time ensuring a good rate of polymerization or copolymerization.
One subject of the invention is thus alkoxyamines of formula: 
in which R1 and R2, which may be identical or different, represent a hydrogen atom, a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 10, an aryl radical, an aralkyl radical containing a number of carbon atoms ranging from 1 to 10, or R1 and R2 are linked together so as to form a ring including the carbon atom bearing said R1 and R2, said ring containing a number of carbon atoms, including the carbon bearing the radicals R1 and R2, ranging from 3 to 8; R3 represents a linear or branched, saturated or unsaturated hydrocarbon-based radical which may comprise at least one ring, said radical containing a number of carbon atoms ranging from 1 to 30; R4 and R5, which may be identical or different, represent a linear or branched alkyl radical, a cycloalkyl, aryl, alkoxy, aryloxy, aralkyloxy, perfluoroalkyl, aralkyl or thioalkyl radical containing a number of carbon atoms ranging from 1 to 20, or R4 and R5 are linked together so as to form a ring including the phosphorus atom, said heterocycle containing a number of carbon atoms ranging from 2 to 6 and possibly also containing one or more oxygen or sulfur atoms;
Z is a cycloalkyl radical containing 3-12 carbon atoms or a residue of formula: 
xe2x80x83in which R6, R7 and R8, which may be identical or different, represent a hydrogen atom, a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 10, a phenyl radical, a benzyl radical, a cyano radical or a cycloalkyl radical containing from 3 to 12 carbon atoms; a radical xe2x80x94(CH2)n-C(O)OR9 in which R9 represents a linear or branched alkyl containing a number of carbon atoms ranging from 1 to 6 and n=0 to 6.
Among the compounds of formula (I), the ones that are most particularly preferred are those in which R1=H, R2=R3=(CH3)3Cxe2x80x94, R4=R5=CH3CH2Oxe2x80x94, Z=C6H5CH2xe2x80x94, (CH3)2C (CN)xe2x80x94(R6=R7=CH3xe2x80x94, R8=NCxe2x80x94), CH3OC(O)C(CH3)2xe2x80x94, (R6=R7=CH3xe2x80x94, R8=xe2x80x94(CH2)nC(O) OR9 with n=0 and R9=xe2x80x94CH3); CH3OC(O)CH(CH3)xe2x80x94(R6=H, R7=CH3xe2x80x94, R8=xe2x80x94(CH2)nC(O)OR9 with n=0 and R9=xe2x80x94CH3); C6F13xe2x80x94, C6H5CH(CH3)xe2x80x94, C6H5C(CH3)2xe2x80x94, C6H12xe2x80x94, CH3(CH2)5xe2x80x94.
The alkoxyamines of formula (I) may be prepared according to methods known in the literature. The most common method involves the coupling of a carbon-based radical with a nitroxide radical. The carbon-based radical Z. may generated by various methods described in the literature: decomposition of an azo compound, abstraction of a hydrogen atom from a suitable substrate, addition of a radical to an olefin. The radical Z. may also be generated from an organometallic compound, for instance an organomagnesium reagent Zxe2x80x94MgX as described by Hawker C. J. et al. in Macromolecules 1996, 29, 5245-5254 or from a halo derivative Zxe2x80x94X in the presence of an organometallic system such as CuCl/bipyridine according to a reaction of ATRA (Atom Transfer Radical Addition) type as described by Dorota Greszta et al. in Macromolecules 1996, 29, 7661-7670.
Among all these methods, the one which will preferably be used to prepare the compounds of formula (I) is the method involving the ATRA reaction.
This method consists in transferring an atom or a group of atoms onto another molecule in the presence of an organometallic catalytic system such as CuBr/bipyridine and in a solvent medium.
The procedure generally used consists in dissolving the organometallic complex such as CuBr/bipyridine in an organic solvent, preferably an aromatic solvent such as benzene or toluene, and then in introducing into the solution the compound ZX and the xcex2-phosphorous nitroxide.
The reaction mixture is then stirred at a temperature of between 20xc2x0 C. and 70xc2x0 C. for a period at least equal to 48 hours, or even longer.
Next, the precipitate is filtered off, rinsed with a solvent such as ether and then washed with an aqueous 5% by weight CuSO4 solution and finally with water.
After drying over MgSO4, the solvents are evaporated off under reduced pressure.
The alkoxyamines of formula (I) according to the present invention may be used for the polymerization and copolymerization of any monomer containing a carbon-carbon double bond which is capable of undergoing free-radical polymerization. The polymerization or copolymerization is carried out under the usual conditions known to those skilled in the art taking the monomer(s) into consideration. The monomers under consideration may be a vinylaromatic monomer (styreree or substituted styrenes), a diene, an acrylic monomer such as methyl acrylate or butyl acrylate or a methacrylic monomer. The monomer may also be vinyl chloride, vinylidene difluoride or acrylonitrile.
The alkoxyamines (1) may advantageously be introduced into the polymerization or copolymerization medium at contents ranging from 0.005% to 5% by weight relative to the monomer(s) used.
The examples which follow illustrate the invention.
The xcex2-phosphorous nitroxide or formula: 
will be used in the examples below and will be denoted as DEPN.
It was obtained by oxidation of diethyl 2,2-dimethyl-1-(1,1-dimethylethylamino)propyl phosphonate using meta-chloroperbenzoic acid according to a protocol described in international patent application
The compounds obtained were characterized by elemental analysis and by 1H, 13C, 31P and 19F NMR.
The NMR spectra were acquired on a Bruker AC 100 machine (1H, 100 MHz; 31P, 40.53 MHz; 19F, 94.22 MHz; 13C, 25.18 MHz). The 13C and 31P NMR spectra are acquired with 1H decoupling.
The chemical shifts xcex4 are given in ppm relative to tetramethylsilane (internal reference) for the proton and carbon, relative to 85% H3PO4 (external reference) for phosphorus and relative to trifluoroacetic acid for fluorine.